going Pass Labs, do I need "Class A " ?

French_fries, Are you saying the XA.5 amps have less control at the frequency extremes than do the X.5 amps? I always thought it was more about bias into class A and the distortion at the crossover point between the positive and negative halves of the signal. (How's that for a non-technical explanation). I'm curious as I'v only heard the XA.5 in my system. Clearly some prefer one line/series over the other, and visa versa.

Thanks for that description, Petrushka. That makes a lot of sense. I think it would also depend in large part on the speakers and how they are voiced. Some are warmer and more relaxing and some are more dynamic and lively, etc. Also, on a listeners personal biases and types of music as you write.

I'd love to directly compare the XA160.5 to the X600.5 in my system. It's tough though with no local dealer and shipping costs for such heavy pieces.

French_fries, So you haven't actually heard these amps? Why comment then?

Unsound, If you mean by "dollar for dollar: yes" one should buy the Class A Pass Labs amps, then I would tend to agree, though I'm sure there are situations where someone would prefer the A/B models. They do sell many of the X.5 amps.

So Unsound, I think I now understand you. Given roughly $15,000, the XA100.5 has less control at the upper and lower frequency extremes than does the X600.5? I was not aware of that.

French_fries, I agree there certainly is a reason for having the two different lines. Both sell well, so people must prefer one over the other. Besides the power rating in Class A, I have not read a description of how they really differ sonically. I had always assumed that an XA160.5 could drive any speaker as well as an X600.5 can, it just is biased more for Class A. Perhaps someone with more experience than me directly comparing these amps can clarify this. I've never had an X or X.5 series in my system.

Regarding the Aleph series versus the XA.5 series: I have owned a few models in each line. The most similarly rated amps that I have owned are the Aleph 2 and XA100.5, both rated class A for 100 watts and both mono blocks. I used each with the Eggleston Rosa speakers (87dB, 5-6 ohm). The XA100.5 was much better in my system. More effortless, lower distortion, quieter, more control over the lower frequencies, better soundstaging. No comparison really. I much prefer the XA.5 in my system. But as I say, I've never tried the X.5 series.

Petrushka, That seems like a good summary, though I haven't heard an X.5 amp
in my system. How would you describe the slightly different voicings? Is the
difference fairly subtle or quite noticeable? Thanks.